Talk:Magnetic resonance imaging

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Hoping that some contributors may notice, I would like to propose one addition here (being not that bold for the moment):

The increasing number of MRI scans ordered has become a significant cost factor for healthcare. Even when a CAT examination would be able to answer the same questions, MRI scans are ordered where available.

Opinions whether this statement is NPOV and may be added? Pjacobi 15:43, 19 Jul 2004 (UTC)

• It may be worth rephrasing, but seems valid to add. It may also be worth noting that unlike CAT, MRI studies don't involve radioactive contrast materials. --Improv 14:30, 21 Feb 2005 (UTC)

Where I work, I feel MRI is in fact underutilized. The radiation dose and contrast load of enhanced CT are serious things. As mentioned above, MRI has neither of these risks, as far as we know, and in many cases -- not all -- provides superior diagnostic information. It is very true that cost and time (MRI is much more time intensive than CT, both in preparation and acquisition) are real factors, but this will only improve in the near future, as it has in CT. I would choose MRI over CT for my family any time I could. xiggelee 02:04, 1 Mar 2005 (UTC)

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"Such open bore magnets are often lower field magnets, typically in the 0.2 Tesla range, which decreases their sensitivity but also decreases the Radio Frequency power potentially absorbed by the patient during a protracted operation."

Is this true? I don't think the field strength of the large coil necessarily has anything to do with the intensity of the RF. - Omegatron 03:38, Feb 14, 2005 (UTC)

The frequency of the RF field is proportional to the main field of the magnet: lower field => lower RF freq. => lower SAR. Also the induced currents into the conducting instruments (such as needles) decrease with lowering of the frequency.

AFAIK, the only outcome of increased deposition of RF energy in a patient is increased heat deposition, and it is on a miniscule order of magnitude -- not enough heat to feel. (Any heat felt during the scan would most likely be from the equipment, not the RF pulse.) Importantly, the signal-to-noise ratio is wildly better on the stronger field magnets (usually 1.5 T). The open bore magnets yield lower quality images. xiggelee 02:04, 1 Mar 2005 (UTC)

Yes, the whole body SAR is typically not a factor at lower fields (excluding very small patients, such as babies). But the localized SAR, for example, at the tip of an antenna-like needle, can easily exceed the SAR limits - Evahala

MRI and depression

Might it be appropriate to mention the anecdotal evidence that MRI can alliviate depression? jScott 06:12, 2005 Feb 21 (UTC)

• I've never heard anything about this, but I'll mention it to my subjects :) Seriously though, unless it's at all a well known belief or happens to be true (I know of no studies on the topic, but I'll do a litsearch when I get to work), I doubt it's worth mentioning. It seems extremely unlikely to me that MRI could affect people that way given the physics involved, although it's possible that the novel experience of being in an enclosed space for the length of a study (or for a medical scan), or being around researchers/doctors, may make people feel better. Even if MRI were, on some off chance, actually capable of affecting things, it would be prohibitively expensive to do frequent treatment with it -- where I work, our scanner is typically backed up for weeks in advance, and costs around $700/hr to run. --Improv 14:30, 21 Feb 2005 (UTC)

• You may be referring to repetitive transcranial magnetic stimulation (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12696999&dopt=Abstract|) (rTMS). I don't know a lot about it, but while it does involve magnetism applied to the brain, it is otherwise a completely different technique than MRI. rTMS produces a transient high-strength rapidly-changing magnetic field in the brain, and it is a treatment alternative to electroconvulsive therapy (ECT). In MRI, the magnetic field is only the background: the magnet aligns the nuclei, an RF pulse knocks them out of alignment, and as they go back, you watch what happens and gather information. xiggelee 02:04, 1 Mar 2005 (UTC)

Spins of atomic nuclei

"When the object to be imaged is placed in a powerful, uniform magnetic field, the spins of the atomic nuclei ..." I may be rusty on NMR, but isn't it the spin of the electrons, and not the nuclei? --jag123 06:22, 1 Mar 2005 (UTC)

Nuclear Magnetic Resonance —jScott 23:47, 2005 Mar 17 (UTC)